The invention relates to a multichamber tank for motor vehicles, the chambers of which meet via a constricted region located high up, a first chamber having a filler neck, and a line bridging the constriction forming the connection to a second chamber. Such fuel tanks are found in motor vehicles with rear-wheel drive, for safety reasons in front of the rear axle, and are shaped in such a way that sufficient space remains free for passage of the propeller shaft leading to the rear axle. This accounts for their shape, because of which they are also designated as saddle tanks.
This shape requires special precautions for drawing in and delivering the fuel to the engine because a single feed pump unit in a single chamber is clearly inadequate. For this purpose, either a number of feed pump units are necessary, one in each chamber, or only one in one chamber and a sucking jet pump in the second chamber. An example of the first arrangement is known from DE 102 08 788 A1, an example of the second arrangement from DE 196 27 578 A1. The filling-up of such containers is dependent on the liquid level in the chamber with the filler neck at some time reaching the vertex of the saddle and the fuel thus passing into the second chamber. If the vertex is very high up, a connecting pipe located low down may additionally be provided between the two chambers; however, this pipe causes great difficulties during tank and/or propeller shaft installation. Another solution consists in equipping both chambers with a filler neck, one on each side of the vehicle.
The problem to be solved consequently consists in level equalization during filling-up. The arrangement between the two chambers of a connecting line bridging the constriction, which makes use of the siphon effect known to every cellarman, is known from WO 02/38409 A1. This line will bring about level equalization between the two chambers without external influence if it contains no air. For this, however, its cross section must not be too large and it must be ensured that the liquid level in the two chambers never falls below the respective opening of the pipe. The latter is achieved according to WO 02/38409 A1 by means of a sucking jet pump, which keeps the connecting line always filled with liquid. However, the sucking jet pump has to be fed from the fuel pump, which has to be taken into account in the design of the latter. The cross section of the connecting line is in any case too small to bring about a level equalization which keeps up with the liquid flow from the gas pump nozzle during filling-up. The two liquid flow rates differ greatly.
It is consequently an object of the invention to equip a fuel tank of the generic type in such a way that both chambers are filled at approximately the same speed during filling-up through a filler neck.